The Train to met Life Stadium only runs for special events, The Siyum is officially a private event. The same holds true for the buses as well, You will need to call NJ transit. Its possible the Coach Company Bus will run from the Port Authority.
Hopefully the Siyum organizers contacted NJ transit , notified them about the Siyum and asked if some public transit could run (At least the buses)
NJTransit doesn’t care if the event is public or private. They have an arrangement with the Meadowlands Complex to provide transportation based on the number of tickets issued.